WASHINGTON - Rep. Kevin Cramer is expected to tap oil billionaire Harold Hamm to be his finance chairman should he run for the Senate, according to two Republicans familiar with the congressman's plans - the latest sign that the North Dakota Republican is moving closer to challenging Democrat Heidi Heitkamp in one of the year's biggest contests.

Hamm, who has been friends with Donald Trump since bonding over his brand of neckties in 2012, is a longtime political donor with a deep Rolodex that would be an asset to Cramer if he challenged Heitkamp.

Hamm and Cramer are already allies. After Trump's surprise 2016 win, the two talkedeach other up for the post of energy secretary. Hamm donated money to help Cramer get elected to the House. Now, Cramer sits on the House Energy Committee.

The Republicans familiar with Cramer's plans spoke on the condition of anonymity to describe private moves and considerations that had not been announced publicly. A Cramer spokesman did not immediately comment, nor did a spokeswoman for Hamm.

In the past week, Republicans have grown increasingly confident that Cramer will reverse his January decision not to run for the Senate, which came after President Trump and other Republican leaders tried to coax him into the race.

But several Republicans familiar with Cramer's emerging plans cautioned that nothing is final until and unless the congressman makes an official announcement. Some GOP leaders had been under the impression the last time he considered the race that he would run, only to see him pull back.

Cramer said Tuesday that he was "respectfully reconsidering" his decision and would make up his mind "by the end of the weekend." He mentioned the sweeping GOP tax overhaul that passed late last year as a factor in his thinking, saying the "enthusiasm for that has grown in the last couple of weeks."

Republicans hold a 51-to-49 Senate majority. The race against Heitkamp is one of their top pickup opportunities; North Dakota is one of 10 states Senate Democrats are defending that Trump won in 2016.

GOP officials have privately worried that without Cramer, they will not be able to field a top challenger against Heitkamp, who has worked hard to cultivate a centrist image.

State Sen. Tom Campbell, a Republican, is running. But he is lesser known than Cramer, who holds North Dakota's only House seat, giving him more visibility at home than most rank-and-file House members enjoy.

Influential party officials and Cramer boosters have kept the pressure on him to run, even after he said he wouldn't do it.

"Kevin Cramer is still the number-one draft pick to run for that Senate seat," said Dan Eberhart, an oil industry executive who has donated to him.

Now that Cramer is back in the mix, Democrats have gone on the attack.

"Anyone who says he's a top recruit is either lying through their teeth or related to him," said Joshua Karp, a spokesman for American Bridge 21st Century, a Democratic-aligned super PAC.

Former North Dakota Republican Party chairman Gary Emineth announced Tuesday that he was ending his Senate campaign, saying that Cramer will run, even though the congressman has made no official announcement.

"I'm not foolish enough to say it's easy," Cramer said Tuesday. "It will not be. It will be a very hard race."